Optic Nerve Compression by an Intracanalicular Meningioma.

THE diagnosis of progressive unilateral visual failure, when occurring as a solitary symptom in association with a visual field defect and when all routine investigations are negative, presents many difficulties. Amongst the conditions to be considered are retinal vascular disease, chronic simple glaucoma, atypical forms of toxic amblyopia, optic neuritis, and optic nerve compression. Meadows (1949) considered that a progressive unilateral visual failure associated with a scotomatous or sector field defect was highly suspicious of intracranial optic nerve compression and merited surgical exploration. The diagnostic problem presented by the case which is now being reported was one of unilateral visual deterioration associated with a centrocaecal scotoma, but with negative findings from all other investigations. It was resolved at craniotomy when a meningioma the size of a grain of wheat was removed from the intra-canalicular portion of the dural sheath of the right optic nerve. Cushing and Eisenhardt (1938) stated that "there has been no indubitable example of a sheath meningioma in which intact nerve has been found on both anterior and posterior aspects of a centrally disposed tumour spindle". The present case, however, is such an example and furthermore is one of the smallest tumours of the optic nerve ever recorded.